The present application relates to a fixation device used to provide a rigid or flexible connection between bones of the human body.
Document US 2006/0085071 A1 discloses an intervertebral implant device including a body with an upper side, an under side and a front surface, in which four bore holes suited to accommodate respective bone screws are formed. The body may be formed of body-compatible plastic material. To provide rigidity and strength to the device, a small front plate made from a metallic material such as titanium or titanium alloy is attached to the front surface. Four bore holes corresponding in position to the respective bore holes of the plastic body are formed in the front plate. The bone screws may each be inserted through the bore holes of the front plate and then also extend through the bore holes of the plastic body.
The bore holes of the front plate are provided with internal threads. These internal threads correspond to external threads provided on the respective heads of the bone screws. In order to enable fixation and compression, the threaded heads are conically shaped, thereby tapering towards the shaft sections of the bone screws.
With regard to such a construction, a problem may arise that the screws may loosen and by application of external forces exerted on the vertebral bodies may slowly be screwed out, which may result in severe damage to adjacent blood vessels, and loosening of the whole implant. For this reason, US 2006/0085071 A1 further proposes to attach a securing plate to the front plate. The securing plate covers respective openings of the bore holes in the front plate and thus secures the bone screws inserted therein. As a consequence, the bone screws cannot be screwed out or fall out.
The number of parts used to implement the above described intervertebral implant device is large and the dimensions of the device may become disadvantageously large. Further, an additional screwing step has to be applied by the surgeon in order to secure the bone screws against falling out.
Document EP 1 280 481 A1 shows an intersomatic implant device comprising a cage which is composed of a sidewall. However, the holes or bores provided in the sidewall of the cage are not shown to accommodate bone screws to be inserted therein.
Based on the foregoing, there is a need to provide an improved intervertebral implant device, which simplifies handling of inserting the device between two vertebral bodies, which increases its stability against external forces once the device has been installed, which also provides an efficient downsizing of the components used and/or which protects the bone screws against being screwed out or falling out in case these are loosened.